1. Field of the Invention
This invention relates to an apparatus and process for generating radiant energy, and is more particularly concerned with a radiant wall structure employed in an industrial oven. The structure includes a radiant wall, the temperature profile of which can be varied along selected areas, by increasing or decreasing the velocity of heated gases passing through a combustion chamber.
2. Description of the Prior Art
Various means have been utilized in the past to generate radiant energy for use, for example, in industrial ovens to cure coatings. In the conventional design of heated air ovens, it has been a common practice to provide the heated air for the oven from an external heater house containing a burner, and which utilized a fan to recirculate the heated air to and from the oven. These heater houses were interconnected to the oven with supply and return air ducts. When incinerators are used in conjunction with conventional ovens to oxidize the volatile organic compounds (VOC's) which are generated in the drying (curing) process, the incinerators are also interconnected to the ovens with external air ducts. In most instances, these ducts to and from the heater houses and/or the incinerator must be insulated. This duct work and the heater houses or incinerators occupy valuable space within the manufacturing facility. The external heater houses and associated duct work increase the mass of the oven that must be heated on each heat-up cycle of the oven. This increases the time from when the oven is started to when it is ready for use. On each cycle of the oven, the energy that is consumed in heating the mass of the oven is lost to the environment during the period the oven cools down. The external duct work and heater houses also increase the exposed surface area of the oven, therefore increasing the transmission losses. Not only is this lost energy costly, but often this necessitates the operation of additional, costly air conditioning apparatus to remove this wasted heat from the work environment.
In many applications of ovens using external heater houses, the recirculating fans operate at a high level of noise, which adversely impacts the working environment. The recirculating fans used in the external heater houses require extensive maintenance and consume large quantities of energy. It is common for each recirculating fan in large oven installations, such as those used in the automotive and truck industry, to require fan motors of 25 horsepower and larger. In a large installation of conventional ovens using heater houses, a typical cost of electric energy to drive the recirculating fans is estimated to be in excess of approximately $500.00 per day, or more than approximately $100,000.00 per year. The recirculating fans and the inherent disadvantage of their use is eliminated by the present invention. Also, all external or remote heater houses and associated duct work is eliminated by the structure disclose herein.
A means for generating radiant energy is disclosed in my U.S. Pat. No. 4,546,553, for a Radiant Wall Oven and Process of Drying Coated Objects. This oven generates radiant energy by igniting a combustible fuel mixture behind the radiant wall, and employing a series of propeller fans to direct the heated gases within a chamber against the radiant wall. The heated gases within the chamber are in a turbulent condition, and therefore, the radiant wall is heated substantially uniformly throughout its entire surface area. While this oven provides an efficient and reliable means for drying coated objects, it is practically impossible to selectively vary the radiant energy emitted by different portions of the wall. Further, the fans which direct the heated gases against the radiant wall have many of the inherent disadvantages previously discussed.
In my U.S. Pat. No. 4,785,552 for a Convection Stabilized Radiant Oven, I disclose an oven in which radiant emitter walls emit radiant energy within a drying chamber, accomplishing highly efficient heat transfer by infra-red radiation. Overhead fans circulate the air within the drying chamber to control the equilibrium temperature of the surface of the object in the oven, and to minimize the variation of the temperature distribution in the oven. To generate the radiant energy, a separate furnace utilizing a gas burner assembly is disposed adjacent to the oven. Blowers force heated gas from the furnace through ducts and into outer plenum cavities. The heated gas is directed under pressure through nozzles, and impinges on the inner surface of a radiant emitter wall. While the temperature of the entire radiant emitter wall can be selectively controlled, there is no means to controlled the radiant energy emitted by selected portions of the wall. Further, the separate furnace and its associated duct work and fans also necessarily incorporate the disadvantages previously discussed.